JNK (c-Jun N-terminal kinase, also known as MAPK8) is a stress-activated serine/threonine protein kinase belonging to the MAPK family. It is activated by cellular stress, inflammatory cytokines, and excitotoxicity, playing complex and context-dependent roles in neuronal survival and death. JNK is particularly implicated in Alzheimer's disease, Parkinson's disease, and other neurodegenerative disorders. [1]
| Property | Value |
|---|---|
| Gene Symbol | MAPK8 (JNK1), MAPK9 (JNK2), MAPK10 (JNK3) |
| Chromosomal Location | MAPK8: 10q11.22, MAPK9: 5q35.1, MAPK10: 4q21.3 |
| UniProt IDs | P45983 (JNK1), P45984 (JNK2), P53779 (JNK3) |
| Molecular Weight | ~46-48 kDa per isoform |
JNK exists as three isoforms: JNK1 and JNK2 are ubiquitously expressed, while JNK3 is predominantly neuronal and is the major isoform implicated in neurodegeneration. [2]
JNK proteins share a central kinase domain flanked by N- and C-terminal regions. The kinase domain adopts a typical bilobal structure characteristic of protein kinases. JNK is activated by dual phosphorylation on a Thr-X-Tyr (TXY) motif within its activation loop, catalyzed by upstream MKK4 and MKK7 kinases. The JNK3 isoform contains a unique 30-amino acid C-terminal extension that may confer neuronal specificity. [3]
JNK is activated through a canonical three-tier kinase cascade:
In the healthy brain, JNK regulates:
JNK is strongly activated in Alzheimer's disease brains, particularly in regions vulnerable to neurodegeneration such as the hippocampus and prefrontal cortex. [5]
JNK directly phosphorylates tau at multiple pathological sites. In AD brains, p-JNK colocalizes with neurofibrillary tangles, and JNK activity correlates with Braak staging. JNK also phosphorylates the microtubule-associated protein tau (MAPT) gene promoter, potentially altering tau expression levels. [4:1]
Aβ oligomers activate the JNK pathway through multiple mechanisms:
JNK3 is the predominant isoform in dopaminergic neurons of the substantia nigra pars compacta and is implicated in Parkinson's disease through multiple mechanisms. [6]
| Compound | Selectivity | Development Stage |
|---|---|---|
| SP600125 | Broad JNK inhibitor | Preclinical |
| JNK-IN-8 | Selective JNK inhibitor | Preclinical |
| CC-401 (CC-930) | JNK inhibitor | Phase 1/2 (inflammation) |
| D-JNKI1 | Peptide inhibitor | Preclinical (neuroprotection) |
JNK inhibitors have been tested in clinical trials for inflammatory diseases (rheumatoid arthritis, COPD) with acceptable safety profiles, establishing a foundation for neurodegenerative applications. However, JNK inhibitors have not yet reached Phase 2/3 trials for AD or PD. [1:1]
| Partner | Interaction Type | Function |
|---|---|---|
| MKK4 | Phosphorylation | Upstream activation |
| MKK7 | Phosphorylation | Upstream activation (primary in neuronal JNK activation) |
| c-Jun | Phosphorylation | Transcription factor activation |
| Bim (BCL2L11) | Phosphorylation | Apoptosis activation |
| Bcl-2 | Phosphorylation | Reduced anti-apoptotic function |
| Tau (MAPT) | Phosphorylation | Cytoskeletal dysregulation |
| ATF2 | Phosphorylation | Transcription factor activation |
| p53 | Phosphorylation | Pro-apoptotic signaling |
Bhujbal SP, Hah JM. Advances in JNK inhibitor development: therapeutic prospects in neurodegenerative diseases and fibrosis. Trends in Pharmacological Sciences. 2025. ↩︎ ↩︎
Moro L, et al. Neuroprotective role of JNK inhibitors in neurodegenerative diseases. Neuroscience and Biobehavioral Reviews. 2023. ↩︎
Reijnders CDAM, et al. JNK-associated stellar photocoagulation in Alzheimer's disease. Cellular and Molecular Neurobiology. 2020. ↩︎
Yoshikawa K, et al. c-Jun N-terminal kinase signaling in tauopathies. Frontiers in Aging Neuroscience. 2023. ↩︎ ↩︎
Manoharan S, et al. JNK pathway in amyloid-beta-induced neurotoxicity. Molecular and Cellular Neuroscience. 2023. ↩︎ ↩︎
Kumar V, et al. JNK pathway in Parkinson's disease: molecular mechanisms and therapeutic targets. Molecular Neurobiology. 2021. ↩︎